Single-pinhole and multi-pinhole SPECT imaging are used increasingly in clinical organ specific studies and preclinical studies using small animals. One advantage of pinhole collimation with magnification is sub-millimeter resolution which is not achievable for parallel-beam SPECT. Multi-pinhole SPECT with overlapping counts is also used to improve sensitivity over single-pinhole SPECT.
In the conventional reconstruction of SPECT data acquired with pinhole systems, the point-spread-function (PSF) is either approximated by analytic equations or a simple volumetric intersection model, or substituted by a sensitivity function which is the integral of the PSF. This results in an inaccurate system matrix and loss of resolution for reconstruction. Efforts have been made to directly measure the system matrix using a point source and to model the PSF using Monte Carlo simulations, but those are very tedious, time consuming approaches and thus somewhat impractical, especially for a system with removable pinhole plates which may need to be calibrated frequently.
Desirable in the art is an improved method of calculating the PSF for a pinhole system in order to improve image resolution.